Here's some quick code I used to set up a quick array of linked lists for a leetcode problem - Merge K Sorted Lists.

Converting arrays to singly-linked LinkedLists (without head or tail).

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/**
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 * Definition for singly-linked list.
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 * function ListNode(val) {
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 *     this.val = val;
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 *     this.next = null;
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 * }
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 */
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let ListNode = function(value) {
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  this.value = value;
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  this.next = null;
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  this.connect = (node) => {
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    this.next = node;
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    return this;
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  }
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}
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let convertArray = (array) => {
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  let nodeMap = array.map((x) => new ListNode(x));
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  return nodeMap.map((x, i, arr) => {
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    if (arr[i + 1]) return arr[i].connect(arr[i + 1])
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  })[0]
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}
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// Input:
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// [
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//   1->4->5,
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//   1->3->4,
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//   2->6
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// ]
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// Output: 1->1->2->3->4->4->5->6
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let testArray = [[1, 4, 5], [1, 3, 4], [2, 6]]
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testArray = testArray.map((x) => convertArray(x));